In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are two modes by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as 160 amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element; which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range.
In the event of current levels above the normal operating level of the thermal overload release, it is desirable to trip the breaker without any intentional delay, as in the case of a short circuit in the protected circuit, therefore, an electromagnetic trip element is generally used. In a short circuit condition, the higher amount of current flowing through the circuit breaker activates a magnetic release which trips the breaker in a much faster time than occurs with the bi-metal heating. It is desirable to tune the magnetic trip elements so that the magnetic trip unit trips at lower short circuit currents at a lower continuous current rating and trips at a higher short circuit current at a higher continuous current rating. This matches the current tripping performance of the breaker with the typical equipment present downstream of the breaker on the load side of the circuit breaker.
In certain situations, an operator of an electrical system may desire to know if a circuit breaker is open, closed or tripped from a remote location. Such circumstances can include applications for maintenance and control. It may also be used in applications to provide synchronizing of several breakers, together with other accessories, to open and close several circuit breakers. One device used for signaling the state of a circuit breaker from a remote location is a signal accessory such as a bell switch or an auxiliary switch. Existing signal accessories currently used have several disadvantages. Some such signal accessory accessories must be installed in the circuit breaker housing behind the main cover and in close proximity to electrically live parts and connections. Other signal accessory accessories require the user to provide terminal connections to the switch wires. Further examples of present signal device accessories are designed to be used with a single circuit breaker frame, i.e., for each current rating of the circuit breaker a specially designed signal device accessory is required.
Thus, there is a need for a signal accessory to signal the state of a circuit breaker from a remote location that can be installed in the main cover of the circuit breaker without exposing the electrically live parts of the circuit breaker. There is a further need for a signal device that can be used with several circuit breaker frame sizes, that is, a single signal accessory that will operate over a wide range of constant current ratings for the circuit breaker. There is an additional need for a signal accessory with which a customer can connect its control wiring directly to the signal device without any additional rewiring. And further, there is a need for a signal device for a circuit breaker that can be installed in a circuit breaker utilizing a common latching protrusion that provides an audible snap fit installation.